Alkylation of benzene



Patented May 1950 ALKYLATION F BENZENE Alexander N. Sachanen, Woodbury,and Philip D.

Caesar, Wenonah, N.

J., assignol's to Socony- Vacuum Oil Company, Incorporated, acorporation of New York No Drawing. Application March 1, 1946, SerialNo. 651,429

s Claims. (01. 260-671) This invention relates to the synthesis ofaromatic compounds of the type which may be produced by a Friedel-Craftsreaction, and is more particularly concerned with a process foralkylating benzene.

' As is well known to those familiar with the art, the Friedel-Craftssynthesis is one of the classical reactions of organic chemistry, and,therefore, it is well understood in the art. In accordance with theFriedel-Craits synthesis, when aromatic hydrocarbons and most of theirsubstituted derivatives except the nitro compounds, are contacted with ahalogen derivative of an organic compound, in the presence of aluminumchloride or an equivalent metallic halide catalyst and under suitablereaction conditions, the aromatic hydrocarbons and most of theirsubstituted derivatives lose a hydrogen atom from the nucleus while thehalogen derivative of an organic compound loses a halogen atom andthetwo radicals condense to yield condensation products. Accordingly,the Friedel-Crafts synthesis is a convenient way for preparing alkylaromatic compounds, aromatic ketones, etc.- The typeof condensationeffected by a Friedel-Crafts synthesis is exemplifled, as is well known,by the following equation, wherein R represents an aromatic radical, Rreprepresents an organic radical, and X represents a halogen atom:

R-H+X-R'. RR+HX More specifically, using the Friedel-Crafts synthesis,benzene may be condensed or alkylated with an alkyl halide to producealkyl benzenes:

Although the Friedel Crafts synthesis provides an effective and directmeans for obtaining alkyl benzenes, the alkyl benzenes thus obtained arerelatively expensive in view of the cost of the metallic halidecatalysts and the expense involved in separating the catalysts from thereaction products. As a result, considerable investigation has beencarried out in an effort to develop syntheses whereby the desiredalkylations are effected in the absence of catalysts.

For example, Nenitzescu et al [Annalen der Chemie, 491, 210-220 (1931)]have found that the more reactive aromatic compounds can be condenseddirectly with a halogen derivative of an organic compound in the absenceof a catalyst. Specifically, they have reported that in the absence ofcatalysts, alkylbenzenes can be condensed with benzyl chloride, thatdiphenyl, napthalene and anthracene can be condensed with benzylchloride, and that di henyl and napthalene can be condensed with benzoylchloride. However, these investigators have reported also that in theabsence of catalysts, and even 7 through the use of high temperatures,1112-1202 F., that benzene cannot be alkylated with alkyl halides, thatbenzene cannot be condensed with benzoyl chloride, and finally, thatbenzene cannot be condensed with benzyl chloride. They have reported theforegoing as follows: In the case of benzene itself, it was not possibleto obtain a condensation with simple alkyl halides such as ethylbromide, propyl chloride and benzyl chloride. With benzene, however, thebenzoyl chloride condenses just as little as the abovementioned alkylhalides.

We have discovered that it is possible to condense benzene with an alkylhalide in the absence of a catalyst.

We have now found that under appropriate conditions of temperature andreaction time, that benzene .can be condensed with an alkyl halide inthe absence of a catalyst.

Accordingly, it is an object of the present invention to provide aprocess for effecting the alkylation of benzene with an alkyl halide.Another object is to provide a non-catalytic or thermal process forproducing alkyl benzenes. A more specific object is to afford a processfor effecting the alkylation of benzene with an alkyl halide in theabsence of a catalyst. A very important object is 'to provide anefficient and relatively cheap process for producing alkyl benzenes.Other objects and advantages of the present invention will becomeapparent to those skilled in the art from the following description.

' Broadly stated, the present invention provides a process for effectingthe alkylation of benzene with an alkyl halide in the absence of acatalyst, which comprises contacting benzene with an alkyl halide undercertain related conditions of temperature and reaction time.

-The'reaction conditions necessary for effecting the synthesiscontemplated herein include temperatures varying between about 400 F.and about 700 F., and reaction times varying between several hours attemperatures approximating the lower limit of the temperature range andabout one minute at temperatures approximating the 1 at a giventemperature, the most desirable reaction time can be readily ascertainedby one skilled in the art, the working ranges of both the temperatureand time of reaction having been indif cated hereinbefore.

The interdependence of the temperature of reaction and reaction time isillustrated by the following tests which were carried out in a 2.8

' liter, high-pressure, stainless steel, rocker bomb. The charge in eachcase consisted of 290 grams of benzene and 53 grams of amyl chloride.

Amyl Benzene Yield Reaction Reaction IIEIun l osunds Per Tempe Timetute, F. Minutes Percent of Inch Grams Theoretical The pressure to beused in the process of our invention may vary between wide limits. Inthis ;connection, it must be noted that Nenitzescu et al. (supra)attempted to condense benzene with alkyl halides at elevatedtemperatures and l and at atmospheric pressure. reaction time of theirattempted alkylation must have been of the order of a fraction of a;second. For example, at atmospheric pressure As a result, the

and a reaction temperature of 523 F., and using a charge of one mole ofeach reactant, it would require approximately 90 liters of reaction tubespace to achieve a reaction time of one hour.

Therefore, if a continuous successful reaction is to be realized using areaction tube of reasonable length, in order to attain a reaction timeof required magnitude, the pressure must be sufficient to ensure a highdensity of reactants Tests have conclusively shown that increasedpressure, other reaction variables remaining the same, does not increasethe yields of alkyl benzenes, and that lowering the pressure renders thedesired alkylation impractical from the standpoint of reaction vesselsize.

Therefore, the pressure to be employed in a continuous reactor of givensize depends upon the time of reaction to be used, which in turn dependsupon, as stated hereinbefore, the temperature of reaction. Hence, itwill'be appreciated that the reaction embodied in the process of thepresent invention will be fully defined by a a recitation of thetemperature range, and of the a t me of reaction range or of thepressure range. Thus, when operating with continuous reaction vessels ofpractical size, using a practical onstream reaction time for thetemperature emon-stream reaction Accordingly, we have found that undertemperature employed may be sufliciently close to the lower limit of theworking range as to require a reaction time of several hours to achievepractical yields of alkyl benzenes. In

view of the foregoing, it follows that a very high pressure would berequired to attain such a reaction time in a reaction vessel ofconventional design.

of economy, however, we prefer to use alkyl ehlorides, and especiallythose containing up to about 12 carbon atoms. Ethyl chloride, butylbromide, heptyl chloride, and isopropyl chloride may be mentioned by wayof non-limiting examples of alkylv halides suitable for the purposes ofour process. The alkyl halide reactant may constitute. as little as 2mol per cent or as much as 98 mol per cent of the charge. In practice,however, we use charges containing an excess, on a mol per cent basis,of the benzene reactant over the alkyl halide reactant, and preferably,charges containing benzene in amounts varying between about 50 mole percent and about 90 mole per cent.

The process of our invention may be carried out as a, batch, continuousor semi-continuous type of operation. Particularly when the process iscarried out on a commercial scale, economic considerations make itpreferable to operate in a continuous manner. For efficient operation,whether the process is carried out on a batch or continuous basis, it isessential that the reactants be intimately contacted with each other.This may be effected in several ways and in apparata which are wellknown in the art.

The following detailed examples are submitted for the purpose ofillustrating modes of carrying out the process of our invention. It isto be understood that the invention is not to be considered as limitedto the specific alkyl halide reactants and to the specific modes orconditions of operation set forth therein. As it will be apparent tothose skilled in the art other alkyl halides and a wide variety of otheroperating conditions within the ranges indicated hereinbefore may beutilized.

Example 1 290 grams of benzene and 54 grams of amyl chloride were placedin a 2.8-liter, high-pressure, stainless steel, rocker bomb. Thetemperature was raised to about 650 F. and the contents of the bomb werekept at this temperature for three hours. The pressure during thereaction was approximately 1500-3000 pounds per square inch. The bombwas then cooled and the contents were removed and distilled. 42 grams ofamyl benzenes were obtained.

Example 2 325 grams of benzene and 50'grams of propyl chloride weretreated as in Example 1. The pressure during the reaction wasapproximately 1500-3000 pounds per square inch. The bomb was then cooledand the contents distilled. About 20 grams of propyl benzene (25% oftheoretical) were obtained.

In general, any alkyl halide containing at least The alkylationcontemplated herein and illustrated in the foregoing, is clearlysuperior to the customary Friedel-Crafts synthesis in that no metalhalide catalyst is required, and inasmuch as the desired alkyl benzenescan be separated easily from the reaction mixture by distillation sinceno metallic halide catalyst is present. It will be apparent therefore,that thepresent invention provides an eflicient and relativelyinexpensive process for producing alkyl benzenes. Alkyl benzenes areuseful as intermediates in various organic syntheses, as solvents and asconstituents of motor fuels.

This application is a continuation-in-part of copending applicationSerial Number 480,372, filed March 24, 1943, now abandoned.

The present invention may be embodied in asoasu other specific formswithout departing from the spirit or essential attributes thereof, andit is therefore desired that the present embodiments be considered inall respects as illustrative and not restrictive, reference being had tothe appended claims rather than to the foregoing description to indicatethe scope of the invention.

We claim:

1. A process for effecting the alkylation of benzene with an alkylchloride containing at least two carbon atoms per molecule, whichcomprises contacting benzene with said alkyl chloride, in the absence ofcatalytic material, at a temperature falling within the range varyingbetween about 400 F. and 700 F., but no higher than 700 F., at apressure of at least about 200 pounds per square inch, and for a periodof time of at least about one minute but sui'iicient to eifect saidalkylation.

2. A process for effecting the alkylation of benzene with an alkylchloride containing at least two carbon atoms per molecule, whichcomprises contacting benzene with said alkyl chloride, in the absence ofcatalytic material, at a temperature falling within the range varyingbetween about 400 F. and 700 F., but no higher than 700 F., at apressure of at least about 1000 pounds per square inch, and for a periodof time of at least about one minute but sumcient to effect saidalkylation.

3. A process for eifecting the alkylation of benzene with an alkylchloride containing at least two carbon atoms and up to about l2 carbonatoms per molecule, which comprises contacting benzene with said alkylchloride, in the absence of catalytic material, at a temperature fallingwithin the range varying between about 400 1''. and 700 F., but nohigher than 700' F'., at a pressure 01' at least about 1000 pounds persquare inch, and for a period of time of at least about one minute butsuflicient to effect said alkylation.

5. A process for effecting the alkylation of benzene with amyl chloride,which comprises contacting benzene with amyl chloride, in the absence ofcatalytic material, at a temperature falling within the range varyingbetween about 400 F. and 700 F., but no higher than 700 F., at apressure of at least about 1000 pounds per square inch, and for a periodof time of at least about one minute but suflieient to effect saidalkylation.

6. A process for effecting the alkylation of henzene with propylchloride, which comprises contacting benzene with propyl chloride, inthe absence of catalytic material, at a temperature falling within therange varying between about 400 F. and 700 F., but no higher than 700F., at a pressure of at least about 1000 pounds per square inch, and fora period of time of at least about one minute but suiflcient to effectsaid alkylation.

ALEXANDER N. SACHANEN. PHILIP D. CAESAR.

REFERENCES CITED The following references are of record in the 'flle ofthis patent:

UNITED STATES PATENTS Number Name Date 1,384,423 Bielouss July 12, 19211,518,182 Cur-me, Jr -e Dec. 9, 1924 1,975,456 Kass et a1 Oct. 2, 19342,316,108 Ruthrufl U Apr. 6, 1943 2,357,978 Schmerling et a1. Sept. 12,1944 2,361,355 Sachanen et al Oct. 24, 1944 2,373,303 Frey et al Apr.10, l945 2,402,092 Schmerling et al. June 11, 1946 Certificate ofCorrection Patent No. 2,506,551 v ALEXANDER N. SACHANEN ET AL.

' It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows:

'- Column 2, line 45, after the word about insert 300 F and about 800 R,

May 2, 1950 preferably, temperatures varying between about;

and that the said Letters Patent should be read with this correctiontherein that the Same may conform to the record of the case in thePatent Oflice. Signed and sealed this 29th day of August, A. D. 1950.

THOMAS F. MURPHY,

Assistant Gammz'ssz'oner of Patents.

1. A PROCESS FOR EFFECTING THE ALKYLATION OF BENZENE WITH AN ALKYL CHOLORIDE CONTAINING AT LEAST TWO CARBON ATOMS PER MOLECULE, WHICH COMPRISES CONTACTING BENZENE WITH SAID ALKYL CHLORIDE, IN THE ABSENCE OF CATALYTIC MATERIAL, AT A TEMPERATURE FALLING WITHIN THE RANGE VARYING BETWEEN ABOUT 400*F. AND 700*F., BUT NO HIGHER THAN 700* F., AT A PRESSURE OF AT LEAST ABOUT 200 POUNDS PER SQUARE INCH, AND FOR A PERIOD OF TIME OF AT LEAST ABOUT ONE MINUTE BUT SUFFICIENT TO EFFECT SAID ALKYLATION. 